Ignition system for fuel burners



Jan. 23,1968

. HAYES IGNITION SYSTEM FOR FUEL BURNERS Filed June 28, 1966 TRS fLz

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- ATTORNEY United States Patent O 3,364,971 IGNITIN SYSTEM FOR FUELBURNERS Thomas E. Hayes, Goshen, Ind., assigner to Penn Controis, Inc.,Wheaton, lll., a corporation of Delaware Filed June 28, 1966, Ser. No.561,198 9 Claims. (Cl. 15S- 28) ABSTRACT F THE DISCLOSURE In a controlfor fuel burners the time required to charge a capacitor limits theattempt to ignite the fuel. Should the attempt be unsuccessful, thesupply of fuel to the burners is terminated. Fail-safe features areprovided for misoperation of the llame detector, causing the timingcapacitor to remain fully charged preventing further attempts to ignitethe fuel. Mechanism is Vprovided for discharging the capacitor for newattempts -to ignite the fuel, which dischanging mechanism differentiatesbetween normal circuit interruption, as for example through thermostaticaction, and between failure to ignite or flame out of the burner.

This invention relates to an ignition system for fuel burners and moreparticularly with respect to such systems which utilize a capacitor totime the igniting operation of the burner.

Attempts have been made in the prior art to provide such systems withcapacitor timed igniting operations, termed trial for ignition, as forexample the U.S. patent to Earl I. Weber, 3,174,534, issued Mar. 23,1965. It is desirable that such ignition systems be of simpleconstruction for reasons of economy in manufacturing and operation andyet provide reliable operation. Since the failure of ignition systems tooperate properly may cause considerable damage it is desirable thatfailure of the control results in its being operated to avconditionwhich stops the feeding of fuel to the burner. Such operation of anignition control may be termed fail-safe operation.

It is, therefore, an object of the invention to provide an improvedignition control system which is of simple, economical construction andyet provides reliable operation.

It is another object to provide such ya control which responds -tomalfunctions of its own components by placing the burner in a safecondition and yet utilize only one control relay.

In carrying out the invention, according to a preferred embodiment, upona call for heat, a first circuit is established for the energizing coilof a control relay through a timing capacitor; the initial chargingcurrent ow through the capacitor providing sufficient energization foroperation of the relay. Operation of the relay energizes fuel deliverymeans to provide fuel for ignition simultaneously with energization ofthe igniter means for igniting such fuel. The capacitor charging -rateis used to time the igniting operation, providing a time contest betweenthe capacitor attaining its charged condition and the fuel ignitingmeans igniting the fuel. Under conditions where the fuel is ignited, theburner flame is detected 4by a photoconductive cell which establishes aholding circuit for the control relay, bypassing the timing capacitorlbut subject to lthe contacts of a demand switch, such as a thermostat.

In the absence of the photocell detecting a flame, the relay releases asthe capacitor arrives at its charged value, completing the trial forignition and ceasing delivery of fuel to the burner.

As part of the fail-safe feature of the control in the event that thephotocell becomes shorted, a second charging circuit for the timingcapacitor is provided. This circuit maintains the capacitor in chargedcondition, preventing energization of the control relay.

The timing capacitor is also maintained in its charged condition,preventing energization of the control relay, under conditions where thephotocell is inadvertently excited during a shutdown period.

Under conditions where the photoconductive cell becomes open circuited,the holding circuit for the control relay cannot be established and thesystem locks out in a safe condition.

A fuse in the relay circuit is selected of the type to open the circuit,if the charging capacitor or a diode in series therewith shortsproducing a steady state current through the coil, but to remain closedwhen subjected to the normal charging current pulse during a trial forignition. This fuse may be termed a slow blow fuse.

A relatively low impedance is provided for shunting connection with thetiming capacitor by a pair of rel-ay contacts which are normally openedfor both the operated and unoperated condition of the control relay.These contacts are designed so as to place the low impedance in shuntingrelation with the timing capacitor to quickly discharge the timingcapacitor only under conditions where the control relay releases due tothe relay circuit being interrupted by the thermostat contacts or atemporary interruption of the applied line voltage. This quick dischargeof the timing capacitor allows immediate restarting of the fuel burnercontrol. However, should the relay release be due to a failure toignite, reenergization of the control relay for another trial forignition cannot be undertaken until the timing capacitor has beendischarged, providing a desired lockout These contacts, therefore,distinguish whether a control relay release is due to normal thermostataction or momentary line voltage interruption or to a flame-out orfailure to ignite.

Features and advantages of the invention will be seen from the above,from the following description when considered in conjunction with thedrawing, and from the appended claims.

In the drawings:

FIG. 1 is a schematic line ldiagram of the ignition control circuits,embodying the invention, with the circuits arranged in across-the-lineform;

FIG. 2 is a simplified diagrammatic representation of a portion of afurnace showing the fuel feeding means, burner, igniter and photocellfor the subject control;

FIG. 3 is a simplified diagrammatic elevational view of a control relayutilized in the circuits of FIG. 1 and including contacts whichdistinguish between different releases of the rel-ay; and

FIG. 4 is a sectional view taken along the line 4 4 of FIG. 3.

For convenience, the invention will be described as applied to anignition system for a liquid fuel burner utilizing a lburner motor andan igniter operated from the secondary of a transformer, it beingunderstood, nevertheless, that the invention is as applicable to otherignition systems including gas burner types.

Referring to FIGS. 1 and 2, L1, L2 designate supply lines connected toany conventional alternating current power source (not shown) forsupplying power to the circuit components. M designates a split phaseburner motor for propelling fuel 8 to a burner B in a furnace 9, forignition, while IGN indicates an igniter for igniting such fuel, theigniter being mounted on furnace 9 in any convenient manner in ignitingrelation to the fuel burner and being energized by an ignitiontransformer designated TRS. RL designates a control relay, while C1designates the ignition timing capacitor. PC designates aphotoconductive photocell which is mounted on furnace 9 to detect theame of the burning fuel 8 at the burner B.

Resistors are generally designated R, while rectifiers are generallydesignated CR, sufx letters being added to distinguish the resistors andrectiers from like components. F designates a fuse of the slow blow typewhich is selected to conduct ignition timing pulses during charging ofcapacitor C1 but to open the charging circuit under conditions where asteady state current of a certain magnitude flows through it. Tdesignates contacts of a snapaction type thermostat located in a spaceto be heated.

Contacts of relay RL bear the same letter designation as the relay withnumeral suflixes added to distinguish one pair of contacts from theother, all contacts being shown for the released condition of the relay.Contacts RL4 of the relay are constructed to distinguish vbetween arelease of relay RL under conditions due to power interruption oropening of thermostat contacts T and a release due to failf ure toignite or llame-out. When relay RL releases due to power interruption orthe snap opening of thermostat contacts T, contacts RL4 vibrate betweenclosed and opened position for a certain time and then remain open.

The relay construction to eiect this will now be described withreference to FIGS. 3 and 4, wherein the relay is shown as a pile-up typecomprising a coil RL mounted on a magnetic frame, generally designated10. Frame includes an armature 12 hinged at 13 for magnetic coactionwith pole face 14A of a pole piece 14 when coil RL is energized. Aspring 16 biases armature 12 upward against the magnetic attraction ofpole piece 14. An actuating bar 17 mounted for movement with armature 12actuates leaf-type spring contacts cantilevered to co-act withassociated stationary contacts, the contact pairs being designated RL1,RL2 and RLS in accordance with their designations in the FIG. lcircuitry.

The contact pair RL4 of FIG. l is shown in FIGS. 3 and 4 as a movablecontact RL4a mounted for movement with armature 12 to co-act with astationary contact RL4b mounted on U-shaped bracket 19. RIAa ispositioned near the free end 1Sa of a leaf spring member 18 which isattached at its other end to armature 12 for movement therewith, Mountedon the free end 18a of spring member 18 is a certain mass 20. Mass 20and spring member 18 are selected to provide a spring-mass which willvibrate at a certain frequency and amplitude under conditions where thepower through coil RL of the pile-up relay is interrupted abruptly, asfor example by the snap separation of thermostat contacts T of FIG. 1 ora power interruption to the circuitry.

Under conditions where the holding voltage through coil RL isinterrupted abruptly, such as by power interruption to the circuits ofFIG. 1 or by the snap opening of thermostatic contact T, armature 12(FIGS. 3 and 4) under the influence of its biasing spring 16, releaseswith a snap, as is characteristic of all but specially designed relays.Such a snap causes oscillation of springmass 18-20 at an amplitudesufficient to vibrate movable contact RL4a into successive engagementwith stationary contact RL4b, thereby, repeatedly connecting lowimpedance shunt R4 (FIG. l) in shunting relationship with timingcapacitor C1. The duration of the oscillation under such snap release ofarmature 12 (FIGS. 3 and 4) is calculated to discharge capacitor C1(FIG. 1) sufficiently to enable relay RL to be re-energized immediatelyshould power be reapplied to its energizing coil.

However, under conditions where the holding voltage of relay RL ispassed through slowly in a decreasing direction, as for example, underconditions where capacitor C1 charges at a decreasing rate, to itscutout value, armature 12 (FIGS. 3 and 4) releases without enough snapto cause contact RL/-la to vibrate to engage contact RL4b suiciently todischarge capacitor C1. Contacts RL4 (FIG. l) of the relay, thus,distinguish between a snap type release of armature 12 (FIGS. 3 and 4)and a slower release. This characteristic is used to provide safeignition operation of the burner, as will be described next.

In one tested embodiment of the invention which operated satisfactorilythe following circuit components were utilized.

Resistors Capacitor Rectifiers R1, R2 (100 kilo-ohms). R3 (I mega-ohm).R4 (500 ohms).

C1 (50 microfarads).

CRI, CRS (IN4005).

CB2 (IN4003).

In operation, assume that thermostat contacts T (FIG.y

motor M, causing it to propel fuel to the lburner for ignition by theigniter IGN which is simultaneously energized through transformer TRS bythe closing of contacts RL1.

Relay RL also separates its contacts RL2 and closes its contacts RLS,preparing a holding circuit for relay coil RL through thermostatcontacts T and photoconductive cell PC. Resistor R2 is selected of suchvalue as to limit current through this holding circuit to a valueinsuicient to operate relay RL but suicient to maintain the relay, ifalready operated, in operated condition provided that the resistance ofphotoconductive cell PC is reduced through its excitation by the burnerflame.

Next assume that the fuel is ignited, exciting photocell PC to reduceits resistance sutliciently to provide a holding current through coilRL. Under such conditions, relay RL remains operated through its holdingcircuit, con- -tinuing operation of the fuel burner subject tosatisfac-V tion of the demand for heat as indicated by thermostatcontacts T.

Now assume instead in the above case that the fuel fails to be ignited.Under such conditions, as capacitor C1 charges to its cut-off value,current flowing .through it and coil RL falls to a value insufficient tomaintain the relay energized. It may, also, be noted that sincephotoconductive cell PC is not excited by a llame, a holding circuit forcoil RL is not established. Relay RL releases, reseparating its contactsits contacts RL1, RLS andreclosing contacts RL2, restoring the circuitto its initial condition. This completes the trial for ignition, theduration of which is timed by the R-C value of the above describedignition circuit through capacitor C1. Reclosing of contacts RL2 iswithout effect, since the resistance of photoconductive cell PC underits unexcited condition is sufficiently high so as to electricallyisolate capacitor C1 and coil RL from supply line L1.

The charged condition of capacitor C1 prevents a second trial forignition -until thermostat contacts T are reopened and capacitor C1discharges sufficiently through resistor R3, thus, providing a safetyperiod after a trial for ignition which resulted in a failure to ignitethe fuel..

Other provisions for fail-safe and reliable operation are included inthe above circuitry. For example, since the only holding circuit whichmay be established for coil RL is through thermostat contacts T,shorting of photocell PC while the fuel burner is in operation causesrelay RL to continue operation of the burner only so long as thethermostat contacts T remain engaged calling for heat. Assuming thatsuch a short circuit occurs and continues after the heat requirement issatisfied, thermostat contacts T reopen, causing relay RL to release, aswas described above. Relay RL'in releasing, recloses its contacts RL2,causing a trickle of current to ow through shorted photoconductive cellPC, resistor R1 and diode CR2 slowly charging capacitor C1 to fullycharged condition. The resistance of resistor R1 is selected to preventsuch current iiow from being of sufficient magnitude to cause relay RLto reoperate. Under such conditions, on the next demand for heat, asthermostat contacts T close, capacitor C1 is already chargedsufticiently to prevent the flow of current through relay coil RL insufiicient magnitude to cause reoperation of the relay. The ignitionsystem is thus safely locked out.

The system also locks out in this manner under conditions of photocellPC being inadvertently excited during periods of no demand by thermostatcontacts T, as for example, by ambient light or an undesired flame atthe burner.

Next assume that photocell PC becomes open-circuited. Under suchconditions relay RL is operated by the initial charging current throughthermostat contacts T and capacitor C1, as was previously described.However, at the end of the trial for ignition, that is, when capacitorC1 charges to its cut-off value, relay RL releases, since the holdingcircuit through photocell PC cannot be established.

Next assume that either rectifier CR1 or capacitor C1 becomesshort-circuited, producing a relatively high steady state currentthrough coil RL. Under such conditions, slow blow fuse F opens,interrupting the circuit for coil RL, causing the ignition system tooperate to a safe condition. As was previously explained, fuse F is suchas to remain conducting under conditions Where the normal charging pulseto capacitor C1 ows through it, but to open the circuit under conditionsWhere a steady current of sufficient magnitude to operate relay RL flowsthrough it.

After an unsuccessful trial for ignition or ame out of the burner,capacitor C1 must discharge through its discharge circuit provided byresistor R3 before another trial for ignition may be attempted. Thisprevents accumulation of fuel in the burner and provides safe operation.This waiting period, however, is not necessary for safety and isundesirable under conditions where an interruption of energizing powerto coil RL is due to a momentary power interruption which quickly stopsthe burner motor M or one due to normal thermostat control. Under Suchconditions, it is desirable to immediately restart burner operation.Under conditions of power interruption or snap opening of thermostatcontacts T, the current flowing through coil RL is stopped abruptlycausing a snap-action release of the relay armature 12 (FIG. 2). Suchsnap action release, as was previously described, causes armature 12 tosnap upward with sufficient force to cause contact RL4a (FIGS. 3 and 4)to vibrate and repeatedly engage contacts RL4b. Such momentary repeatedclosing of contacts RIA (FIG. 1) connects resistor R4 in shuntingrelationship across timing capacitor C1 immediately dischargingcapacitor C1. The oscillations of spring-mass 1820 (FIGS. 3 and 4)quickly dampen to place contacts RL4a and RL4b in their normally openposition. This places the ignition control circuit in condition forimmediate restarting of the fuel burner without the aforementionedcapacitor discharge waiting period and lock out.

It may be noted that the low impedance shunt for quickly dischargingcapacitor C1 need not be a resistor but may instead be a secondcapacitor (not shown) for capacitor C1 to discharge into.

It is, thus, seen that the subject ignition control is of simple andeconomical design, yields reliable operation and automatically respondsto malfunctions of its own circuit components for operating to a safecondition, thereby, maximizing its ability to control ignition ofburners safety.

As changes can be made in the above described construction and many moreapparently different embodiments of this invention can be made withoutdeparting from the scope thereof, it is intended that all matter 6contained in the above descripition or shown on the accompanying drawingbe interpreted as illustrative only and not in a limiting sense.

What is claimed is:

1. A control for a fuel burner including means for feeding fuel to aburner and an electric igniter energizable and positioned for ignitingat said burner said fuel, said control comprising;

a source of A.C. power,

a control relay including actuating coil and diode means constructed andarranged to enable operation of said relay from said A.C. power source,

a capacitor,

fuel demand means including switch means for electrically connectingsaid power source and said capacitor into energizing electrical relationwith said control relay coil and diode means for actuating said controlrelay,

flame detecting means having a normally high resistance which decreasesto a relatively low resistance when it detects flame, said flamedetecting means being positioned to detect the dame vof fuel burning atsaid burner,

a first current limiting resistor interconnecting said flame detectingmeans in series circuit with said control relay coil and diode means,said first resistor being of such value as to limit current flow throughsaid relay coil and diode means under said low resistance conditions ofsaid flame detecting means to below the pull in value but above the holdin value of said relay,

a diode and a second current limiting resistor electrically connectingsaid ame detecting means in a charging circuit for said capacitor, saidsecond resistor being selected of such value as to limit current to saidcapacitor to less than the pull in value of said control relay forcharging said capacitor under conditions where said flame detectingmeans is of negligible resistance,

and circuit transfer means controlled by said relay for,

upon operation of said control relay, electrically disconnecting saidcharging circuit of said capacitor and instead connecting said flamedetecting means-resistor series circuit through said demand switch tosaid power source to establish a holding circuit for said relay, and forreconnecting said detecting means-resistor series circuit to said powersource by shunting said demand switch upon release of said relay.

2. A control as set forth in claim 1 wherein said ame detecting means isa photoconductive cell.

3. Control apparatus as set forth in claim 1 wherein said demand meansis a thermostat positioned in a space heated by heat generated by saidfuel burner.

4. Control apparatus as set forth in claim 1 wherein said transfer meanscomprises switching contacts of said control relay.

5. Control apparatus as set forth in claim 1 wherein said control relayincludes contacts for controlling energization from said power source ofsaid fuel feeding means and said igniter means.

6. Control apparatus as set forth in claim 1 wherein there is alsoprovided a low impedance shunt connectable in shunting relation to saidcapacitor,

and wherein there is provided circuit interrupting means subject torelease of said control relay for connecting said shunt across saidcapacitor,

said circuit interrupting means comprising contact means normally openfor both the operated and released condition of said relay butconstructed to differentiate between a relatively snap type release ofsaid relay and a slower release by vibrating into successive closedmomentary engagement only under conditions of said snap release.

7. Control apparatus as set forth in claim 1 wherein there is, also,provided a discharge circuit of substantially negligible resistance forsaid capacitor,

and wherein there is provided means for selectively connecting saiddischarge circuit into shunting relation with said capacitor, saidconnecting means including a spring mass actuatable by the release ofsaid relay, a movable contact mounted on said spring mass for movementtherewith, a stationary contact mounted for coaction with said movablecontact, said spring mass being selected for causing successivemomentary engagement or" said movable contact with said stationarycontact under conditions Where said spring mass is actuated by a snaptype release of said relay but to avoid such momentary engagement underconditions of a relatively slower release of said relay. S, Controlapparatus as set said relay includes an armature,

and wherein said vibrating contact means include an elongated springmember cantilevered from said armature for movement therewith, and amovable contact positioned near the free end of said cantilevered springmember,

forth in claim 6 wherein a predetermined mass attached to said free end,and

a second Contact stationarily positioned in relation to said movablecontact for coaction therewith under conditions where a snap release ofsaid armature causes suicient oscillation of said spring member, massand movable contact to vibrate said movable contact into successivemomentary engagement with said stationary contact.

9. Control apparatus as set forth in claim 1 wherein there is providedcurrent sensitive circuit interrupting means in series with said controlrelay coil, said current sensitive means being selected to conduct thenormal coil energizing current pulse flowing through said capacitor andsaid control relay coil but to interrupt current flow through said coilunder conditions of steady state en' ergizing current ilow.

References Cited UNITED STATES PATENTS 3,042,107 7/1967 Burckhardt158-28 3,174,528 3/1965 Staring 158-28 3,304,989 2/1967 Alexander et al.15S- 28 JAMES W. WESTHAVER, Primary Examiner.

